Neisseria is a genus of Gram (−) bacteria included among the proteobacteria, a large group of Gram-negative bacteria. Neisseria are diplococci and the genus includes the species N. gonorrhoeae (also called the gonococcus), which causes gonorrhea, and N. meningitidis (also called the meningococcus), one of the most common causes of bacterial meningitis and the causative agent of meningococcal septicaemia. There are over 100 million new cases of gonorrhea annually, making N. gonorrhoeae the second most common sexually transmitted infectious bacterium. A closely related organism, N. meningitidis can cause a number of diseases, such as meningitis, fulminant septicemia, and bacteremia. Antimicrobial resistance and decreasing susceptibility of Neisseria species to extended-spectrum drugs has underscored the need for the development of new antibiotics that target pathogenic organisms in this genus.
Francisella is a genus of Gram (−) bacteria that are coccobacillary or rod-shaped, non-motile organisms, which are also facultative intracellular parasites of macrophages. F. tularensis causes tularemia (also known as rabbit fever). F. novicida and F. philomiragia are associated with septicemia and invasive systemic infections. The preferred course of treatment for tularemia is antibiotic therapy. F. tularensis is naturally resistant to β-lactam antibiotics such as penicillin. Aminoglycosides, such as gentamicin and streptomycin are effective, but are only used in severe cases because these drugs are nephrotoxic. Alternatively, members of the fluoroquinolone or tetracycline drug families can be used to treat tularemia. However, there is a high incidence of relapse (up to 15%) and treatment failures when using these drugs. F. tularensis is a highly infectious and deadly pathogen, and is classified by the CDC as a Category A bioterrorism agent. Inhalation of a single bacterium results in an acute pneumonia with a 30-60% mortality rate without treatment. The intentional development and release of antibiotic resistant strains of F. tularensis could be disastrous. Since a vaccine against tularemia licensed for human use does not exist, we are even more vulnerable to the consequences of bioterrorism.